Human auditory development is characterized by a puzzling structural-functional paradox: infants show sophisticated auditory capabilities from the time they are born despite significant immaturities that exist in their central auditory system. These early auditory skills play a critical role in infants? ability to acquire language, appreciate music, and navigate the complex acoustic environments around them. The neural mechanisms that support early sound processing, however, are not well understood. In the mentored K99 phase of this award, the candidate will employ magnetoencephalography (MEG) to obtain functional measures of auditory processing in infants at different stages of anatomical maturation. The candidate will first test the prevailing hypothesis that early auditory perception is supported predominantly by subcortical processing with a transition to cortical mechanisms after six months of age (AIM 1). MEG responses will be recorded in infants to speech sounds and a complex nonspeech control stimulus. The sources of the MEG signals will then be localized with the equivalent current dipole model. Next, the candidate will characterize the development of functional specialization of speech processing using the late-field MEG responses recorded in the previous conditions (AIM 2). While left hemisphere dominance for speech has been well documented in adult listeners, how this functional asymmetry develops is unclear. Finally, in the independent R00 phase, infants with a mild-to-moderate hearing impairment will be tested to investigate the impact of abnormal auditory experience on central auditory maturation (AIM 3). This research will advance our understanding of the neural mechanisms underlying early sound processing and the role of auditory experience in their development. These findings will also contribute to our understanding of the mature neural networks involved in auditory processing and give context to investigations conducted in older children and adults. From a clinical perspective, this research has the potential to show that early identification and treatment of hearing loss is important for auditory brain development and could serve as the evidence-base for clinical recommendations. The research performed and training provided during this award will enable the candidate to achieve the candidate?s goal of developing an independent research program that employs both neurophysiological and behavioral approaches to investigate typical and atypical auditory development. The independent phase of the NIH Pathway to Independence Career Development award will be carried out at the University of Washington, Seattle, where the candidate will begin her career as a research assistant professor in the Department of Otolaryngology on July 1, 2020.